NAME SERVICE OVERVIEW
When you're logging in to your computer, you need to access your account details, and as you run programs you need to identify other resources such as host computers on your network and further afield.
These resources are made available to you through NAME SERVICES.
For a stand-alone system, you would use a built-in name service which simply accessed the data you wanted in plain text files. However, stand-alone systems are rare indeed these days, and you'll probably use several services
Local files are still useful for basic data such as the administrator's (root) login, which should be defined locally; ideally, you should have a separate root password for each system, and you'll certainly need such an account for occasional and emergency access to the system if the network has failed. Similarly, the host's own name and IP address will be stored locally so that it knows its own name and how to connect to networks.
NETWORK INFORMATION SERVICE
Originated by Sun Microsystems, the Network Information Service provides for the provision of a master and slave servers to provide information on a wide range of databases such as hosts, users, service, email aliases, etc ... and you can add your own databases too if you wish.
Known in its very early days as "yellow pages" - that's why all the file names start with "yp" - NIS provided an excellent tool for administering the various databases centrally. However, it did not provide a distributed administration capability, and this and other issues lead Sun to introduce a new service called NIS+ or nisplus. NIS+ didn't really catch on though.
LIGHTWEIGHT DIRECTORY ACCESS PROTOCOL
LDAP organises data into a hierarchy, allowing it to be administered based on company, branch, department or any other method you choose. Like with NIS, you can provide and serve a wide variety of data through LDAP, and it has become something of a standard with medium sized and larger organisations.
As well as the OpenLDAP server that's distributed with Linux, commercial vendors such as Novell and Microsoft are using the LDAP protocols within their Active Directory and eDirectory products.
Although LDAP can be set up and operated from command line tools via text files (a method we can teach you), you'll find more practically that it's used with graphic tools and editors such as
DOMAIN NAME SERVICE
The Domain Name Service - DNS - (or BIND - the Berkeley INternet Domain) is used to resolve a narrow range of services on a wider (usually worldwide) basis, based on your fully qualified domain name; typically, the two services provided are for host name resolution and mail forwarders - i.e. where to send emails for a domain.
CHOOSING YOUR NAME SERVICES
Once you've got any appropriate name servers running (see separate training modules), you need to tell each individual user system where it's to look for which service.
The main control file is /etc/nsswitch.conf in which you list which service(s) are to be used for which type of lookup. Here's a sample nsswitch.conf file:
# An example Name Service Switch config file. This file should be
# sorted with the most-used services at the beginning.
# The entry '[NOTFOUND=return]' means that the search for an
# entry should stop if the search in the previous entry turned
# up nothing. Note that if the search failed due to some other reason
# (like no NIS server responding) then the search continues with the
# next entry.
# Legal entries are:
# compat Use compatibility setup
# nisplus Use NIS+ (NIS version 3)
# nis Use NIS (NIS version 2), also called YP
# dns Use DNS (Domain Name Service)
# files Use the local files
# [NOTFOUND=return] Stop searching if not found so far
# For more information, please read the nsswitch.conf.5 manual page.
# passwd: files nis
# shadow: files nis
# group: files nis
hosts: files dns
networks: files dns
automount: files nis
Beyond the nsswitch.conf files, there may be a few other settings to make in relation to individual services; since one server will typically look after numerous clients, configuration at the client is kept to a minimum with server side configuration being the more complex.
See also Naming Services overview
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